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- Snugly enclosed within the middle mediastinum (medial cavity of the thorax)
- Contains the heart, pericardium, vessels to & from the heart & lungs, trachea & esophagus.
- M.Mediastinum – located in the inferior mediastinum (lower than the sterna angle)
- Extends obliquely from 2nd rib à 5th intercostals space.
- Anterior to Vertebrae
- Posterior to Sternum
- Flanked by 2 lungs
- Rests on the diaphragm
- 2/3 of its mass lies to the LHS of the midsternal line.
The Pericardium: (Coverings of the Heart)
- A double-walled sac
- contains a film of lubricating serous fluid
- 2 Layers of Pericardium:
- Tough, dense connective tissue
- Protects the heart
- Anchors it to surrounding structures
- Prevents overfilling of the heart – if fluid builds up in the pericardial cavity, it can
- inhibit effective pumping. (Cardiac Tamponade)
Serous Pericardium: (one continuous sheet with ‘2 layers’)
- Parietal Layer – Lines the internal surface of the fibrous pericardium
- Visceral Layer – (aka Epicardium) Lines the external heart surface
Layers of the Heart Wall:
- Visceral layer of serous pericardium
- Muscle of the heart
- The layer that ‘contracts
- Lines the chambers of the heart
- Prevents clotting of blood within the heart
- Forms a barrier between the O2 hungry myocardium and the blood. (blood is supplied via the coronary system)
Fibrous Skeleton of the Heart
- The network of connective tissue fibers (collagen & elastin) within the myocardium
- Anchors the cardiac muscle fibers.
- Reinforces the myocardium
- Flat sheets separate atriums, ventricles & left and right sides of the heart.
- Electrically isolates the left & right sides of the heart (conn. Tissue = non-conductive)
- Important for cardiac cycle
- (interatrial septum/atrioventricular septum/interventricular septum)
- Rings around great vessel entrances & valves
- stop stretching under pressure
Chambers & Associated Great Vessels
2 Atrias (superior): [Atrium = Entryway]
- Thin-walled Receiving Chambers
- On the back & superior aspect of the heart.
- Each has a small, protruding appendage called Auricles – increase atrial volume.
- Septal Area
- Connective tissue dividing L & R atria. (Site of Foetal Shunt Foramen ovale)
- Right Atrium:
- Smooth internal posterior wall
- Where veins drain into (either from body/lungs)
- Ridged internal anterior wall – due to muscle bundles called Pectinate Muscles.
- Blood enters via 3 veins:
- Superior Vena Cava
- Inferior Vena Cava
- Coronary Sinus (collects blood draining from the myocardium)
- Left Atrium:
- Smooth internal post. & ante. walls.
- Blood enters via:
- The 4 pulmonary veins (O2 blood) [Pulmonos = Lung]
2 Ventricles (inferior): [Vent = Underside]
- Thick, muscular Discharging Chambers
- The ‘pumps’ of the heart
- Trabeculae Carnea [crossbars of flesh] line the internal walls
- Papillary Muscles play a role in valve function.
- Right Ventricle:
- Most of the heart’s Anterior Surface
- Thinner – responsible for the Pulmonary Circulation – Via Pulmonary Trunk
- Left Ventricle:
- Thicker – it is responsible for the Systemic Circulation – Via Aorta
- Most of the heart’s PosteroInferior Surface
Landmarks of the Heart:
- Coronary Sulcus (Atrioventricular Groove):
- Encircles the junction between the Atria & Ventricles like a ‘Crown’ (Corona).
- Cradles the Coronary Arteries (R&L), Coronary Sinus, & Great Cardiac Vein
- Anterior Interventricular Sulcus:
- Cradles the Anterior Interventricular Artery
- Separates the right & left Ventricles anteriorly
- Continues as the posterior Interventricular Sulcus.
- Posterior Interventricular Sulcus:
- Continuation of the Anterior Interventricular Sulcus
- Separates the right & left Ventricles posteriorly
Pathway of Blood Through the Heart:
The systemic and pulmonary circuits:
- The right side of the heart pumps blood through the pulmonary circuit (to the lungs and back to the
- the left side of the heart).
- Blood flowing through the pulmonary circuit gains oxygen and loses carbon dioxide,
- indicated by the color change from blue to red.
- The left side of the heart pumps blood via the systemic circuit to all body tissues and back to the
- the right side of the heart.
- Blood flowing through the systemic circuit loses oxygen and picks up carbon dioxide (red to
- blue color change)
- The myocardium’s own blood supply
- The shortest circulation in the body
- Arteries lie in the epicardium – prevents the contractions inhibiting blood flow
- There is a lot of variation among different people.
- Encircle the heart in the coronary sulcus
- Aorta – Left & Right coronary arteries
- Left Coronary Artery – 2 Branches:
- 1. Anterior InterVentricular Artery (aka. Left Anterior Descending Artery …or LAD).
- Follows the Anterior InterVentricular Sulcus
- Supplies blood to InterVentricular Septum & Anterior walls of both Ventricles.
- 2. Circumflex Artery
- Follows the Coronary Sulcus (aka. AtrioVentricular Groove)
- Supplies the Left Atrium & Posterior walls of the Left Ventricle
- Right Coronary Artery – 2 (‘T-junction) Branches:
- 1. Marginal Artery:
- Serves the Myocardium Lateral RHS of Heart
- 2. Posterior Interventricular Artery:
- Supplies posterior ventricular walls
- Anastomoses with the Anterior Interventricular Artery
- Venous blood – collected by the Cardiac Veins:
- Great Cardiac Vein (in Anterior InterVentricular Sulcus)
- Middle Cardiac Vein (in Posterior InterVentricular Sulcus)
- Small Cardiac Vein (along Right inferior Margin)
- – Which empties into the Right Atrium.
- Ensure unidirectional flow of blood through the heart.
- 2x AtrioVentricular (AV) (Cuspid) Valves:
- Located at the 2 Atrial-Ventricular junctions
- Prevent backflow into the Atria during Contraction of Ventricles
- Attached to each valve flap are chordae tendinae (tendonous cords) “heart strings”
- Anchor the cusps to the Papillary Muscles protruding from ventricular walls.
- Papillary muscles contract before the ventricle to take up the slack in the chordae tendinae.
- Prevent inversion of valves under ventricular contraction.
- Right AV Valve:
- The “Tricuspid Valve”
- 3 flexible ‘cusps’ (flaps of endocardium + Conn. Tissue)
- Left AV Valve:
- The “Mitral Valve” or “Biscupid Valve”
- (resembles the 2-sided bishop’s miter [hat])
- 2x SemiLunar (SL) Valves:
- Guard the bases of the large arteries issuing from the Ventricles.
- Each consists of 3 pocket-like cusps resembling a crescent moon (semilunar = half moon)
- Open under Ventricular Pressure
- Pulmonary Valve:
- Between Right Ventricle & Pulmonary Trunk
- Aortic Valve:
- Between Left Ventricle & Aorta
- 1. “Lubb”:
- Sound of a Cuspid Valve closing
- 2. “Dupp”:
- Sound of a Semilunar Valve Closing
- Where to Listen: